The detection of physiologically-important molecules, such as metabolites, in a biological sample can be critical for monitoring a condition or a disease state of a subject. For example, the monitoring of glucose can be used to diagnose and manage diabetes, where maintaining blood glucose within a normal range of 70 mg/dL to 120 mg/dL with insulin therapy and increased glucose monitoring can improve the long-term prognosis of subjects suffering from diabetes, including Type 1 and Type 2 diabetes. Glucose levels alone, however, often do not provide sufficient information for understanding the metabolic processes underlying diabetes and its development. The monitoring of other metabolites, such as fatty acids, can provide an additional understanding of the events leading to the development of a pre-diabetic state or insulin resistance in a subject suffering from diabetes, particularly Type 2 diabetes. Similarly, energy metabolites, such as lactate, a byproduct of moderate exercise, can be monitored to assess the energy expenditure, exercise burden, or fatigue level of a subject.
One method for detecting metabolites, such as glucose, fatty acids, and lactate, in a biological sample includes conjugating a fluorescent dye with a binding member, e.g., a binding protein, that has an affinity and specificity for a ligand or analyte, e.g., a metabolite of interest, and measuring a change in fluorescence upon ligand binding. Although fluorescence-based detection systems can be reliable, they can require sophisticated instrumentation and costs associated with such systems can be high. Thus, there is a need in the art for simple, cost-effective sensors for detecting metabolites, such as glucose, in biological samples. The presently disclosed subject matter addresses, in whole or in part, these and other needs in the art.